Romina Sisti

Durability of GFRP grids for masonry structures

The application of Textile Reinforced Mortars (TRMs) may cause a significant increase of the lateral capacity of unreinforced masonry elements. This paper presents relationships between the durability and the governing material properties of GFRP (Glass Fibre Reinforced Polymers) grids used to produce TRMs. Measurements of the tensile strength were made using specimens cut off from GFRP grids before and after ageing in aqueous solution and high cycle fatigue testing with a number of cycles of 60,000, 150,000 and 300,000. The tensile strength of two GFRP grids was tested after up to 210 days of storage in deionised water and NaCl solution. A degradation in tensile strength up to 30.2% and 10.8% was recorded for the specimens subjected to treatment in aqueous solution and to high cycle fatigue testing, respectively. This degradation indicated that extended storage in a wet environment may cause significant decreases of mechanical properties.

Damage assessment and the effectiveness of prevention: the response of ordinary unreinforced masonry buildings in Norcia during the Central Italy 2016–2017 seismic sequence

Four regions of central Italy were struck by the seismic sequence of the 2016 earthquake in the country: Lazio, Abruzzo, Umbria and Marche. This highlighted the different behaviour of masonry constructions depending on the prevention actions carried out after previous earthquakes. In particular, although damaged, the masonry buildings in the historical centre of Norcia (Umbria region) behaved significantly better than those in other regions. Indeed, the strengthening interventions carried out after the earthquakes of 1971, 1979 and 1997 greatly affected the seismic behaviour of masonry aggregates (contiguous masonry structural units, MSUs) in the historical centre, which sustained limited damage and a low number of collapses. This paper discusses the empirical data on damage collected with respect to 670 MSUs by means of the first level survey form concerning post-earthquake damage, and usability assessments (AeDES). The forms completed for the survey relate to MSUs in the historical centre of Norcia and were produced by the technicians of the Umbria Seismic Risk Office. The analysis shows the correlation between the MSU characteristics of: age of construction and renovation work; type of vertical and horizontal structures; roof types and usability rating; and the damage level and extent thereof detected in vertical structures. The effectiveness of previous strengthening interventions and the analyses of the types of strengthening solution are also discussed. A case study aggregate is analyzed in detail in order to illustrate the importance of strengthening interventions on vertical bearing elements. The strengthening interventions resulted in a sound strategy to strongly reduce losses, even in a very vulnerable centre comprised of old residential masonry aggregates.

A numerical study on seismic damage of masonry fortresses

Abstract Studies oriented to restoration and conservation of historical monumental buildings have recourse to structural analysis as a way to investigate the genuine structural features of the construction, to better understand its present condition and actual causes of existing damage, to estimate its safety conditions and to determine necessary remedial measures. Based on this background, this paper discusses on the seismic vulnerability of masonry fortresses by means of an analysis methodology based on three different analytical procedures, according to an increased knowledge of the structure. As a relevant case study the Albornoz fortress, a 14th stone masonry construction located in central Italy, was selected. Initially, the strategy proposed to perform this task was aimed at testing and developing an expeditious and non-destructive procedure to evaluate both the seismic vulnerability and the main mechanical properties of the different masonry typologies. The macroscale structural behavior of the fortress was then evaluated through a nonlinear static analysis (pushover) and a more simple approach based on the kinematic theorems of the limit analysis. From this point of view, by comparing the capacity of the construction to withstand lateral loads with the expected demands resulting from seismic actions, these methods provided a highly effective means of verifying the safety of the masonry structure and its vulnerability to extensive damage and collapse.

Analysis of the collapse mechanisms of medieval churches struck by the 2016 Umbrian earthquake

ABSTRACT The 2016 Umbrian earthquake caused the collapse of several medieval churches, while it was noted that ordinary buildings only reported moderate or little damage. Researchers and technicians are looking to these religious constructions with the aim of understanding their structural behavior under seismic action. Depending on the direction of the seismic action, the typical collapse mode was the overturning of the side walls or of the church façade. This often produced the collapse of the roof structure. In many situations, the overturning was facilitated by a weak connection between the load-bearing walls. In this article, the collapse modes of three mediaeval churches are investigated. The article goes into some detail about what considerations are relevant when analyzing a historic masonry construction. The churches object of this study are located in Campi, a hamlet of Norcia, Italy. Between 2000 and 2004, a research team from the Technical University of Milan in collaboration with the Italian Ministry of Culture carried out an extensive investigation on the historic buildings of Campi, providing interesting data about the maintenance level and a summary of the structural state of the churches. These data were used in this article for a critical analysis of the causes of collapse, performed in combination with numerical simulations of the global behavior and local instability.

Seismic Assessment of the Palace of Priors in Perugia

The seismic assessment of historical structures necessitates considering conservation and safety objectives as well as the possible presence of cultural heritage assets. To this end, this paper emphasises the results of a seismic evaluation procedure carried out by the authors on an illustrative case of study, the Palace of Priors in Perugia, that in addition to being one of the most important local governor buildings built, during the High Middle Ages, by Italian communes of Central Italy, it is characterized by the presence of a lot of artistic assets as well. Within this context, strong emphasis was placed on the seismic risk assessment of the structure carried out with reference to the Italian guidelines for heritage protection and conservation. More specifically, the paper investigates and critically discusses the seismic response of the building by using 3 different types of evaluation: territorial level analysis (LV1), local level analysis (LV2) and global level analysis (LV3).

Seismic analysis of artistic assets: the Piero della Francesca’s fresco called “Resurrection”

Traditional construction techniques in seismic areas have been characterized, for a long time, by a large variety of structural solutions based on the combined use of masonry and timber elements. Examples of this can be found also in Nepal, where the recent seismic event occurred on April 25th, 2015 has made the analysis of the traditional building technology very urgent. The interest for this comes from the consideration that the Newari vernacular architecture, developed in the Kathmandu valley, presents interesting earthquakeproof structural solutions, very different from the typical timber frame adopted in other nearby regions, like the Kashmir Dhajji-dewari. Through the analysis of the effects produced by the recent earthquake on vernacular structures in Nepal, this research aims at clarifying both the current state-of-the-art and the capabilities of the Newari architecture, which is nowadays subject to the risk of disappearing and needs therefore to be understood in order to preserve its identity and to improve restoration projects.

Seismic vulnerability of the Piero della Francesca’s fresco called “Resurrection"

The structural analysis of monumental buildings requires to consider safety and conservation objectives, including also the possible presence of artistic assets. In order to face these issues, the paper presents an account of the results of diagnostic analyses conducted by the authors on a specific monumental masonry building: the Civic Museum of Sansepolcro, a small town near Arezzo; in fact, besides to be one of the most renowned civic structures built by Italian communes of Central Italy during the High Middle Ages to house their city governments, it is also characterized by the presence of Piero Della Francesca’s fresco, known as “Resurrection”, that is widely hailed as one of the masterpieces of late 15th-century Italian art. Within this context, the integrate use of three different modelling strategies of different complexity is discussed: the equivalent frame approach, the macro-block model and the finite element model. In the first part, a full 3D pushover analyses and a simplified approach based on the kinematic theorem of limit analysis are used in order to understand the large-scale structural performance of the building. Next, the results of the finite element method (FEM) tests conducted on a detailed 3D model of the wall containing the Piero Della Francesca’s fresco are employed in order to investigate the origin of the surveyed crack pattern on this important artistic asset.

Ageing problems of GFRP grids used for masonry reinforcement

In this study, an effort was made to develop an experimental protocol to study the effects of accelerated ageing on GFRP (Glass Fiber-Reinforced Polymer) grids. The physic-mechanical properties of different types of glass FRP grids were investigated. GFRP specimens were subjected to environmental agents including freeze-thaw, high relative humidity, high temperature. Mechanical and physical tests were used to measure the retained properties and to observe the causes of damage and strength reduction. The experimental data showed that resin properties may strongly influence the durability of FRP reinforcement, environmental combined cycles did not take to significant damage of conditioned specimens; GFRP grids are sensitive to alkaline attack when resin does not provide adequate protection to fibers.